Conventionally, as a sealing device for use in a rolling bearing apparatus (a hub unit) for a wheel, there is, for example, a sealing device that is mounted in an annular space defined between an inner member and an outer member which rotate relative to each other. This sealing device includes a slinger which is press fitted on the inner member and a seal main body which is press fitted in the outer member, and this seal main body is made up of a core metal which is press fitted in the outer member and a seal member which is fixed to the core metal and which has a main lip, an auxiliary lip and a side lip which contact closely and slidably the slinger (for example, JP-UA-4-50724).